Centrifugal separators with a sealed inlet usually need to drain off air or other gas from the inlet in order to enable free passage of the incoming liquid mixture that is to be separated. This may be especially noticeable when the inlet flow is introduced in a separator that is already running at its operational speed. The first amount of liquid may form a “stench trap” in the bowl and thereby stopping the gas trapped at the inlet from passing through the bowl. Trapped gas may in turn obstruct, partly or even totally, the liquid flow through the separator. This may of course be a setback for sealed separators, but trapped gas may sometimes be forced through the separator by increasing the inlet pressure temporarily. Since this may not always be possible, some separators may be equipped with a small passage that allows blocking gas to escape, internally in the separator, from the inlet to the outlet and thereby allowing inlet liquid to flow freely at the inlet. The drawback may be that not only gas may pass through such a passage, but also unseparated liquid that is then fed directly to the clean and separated liquid at the outlet. At low flow rates and with high demands of separation efficiency, this may not be acceptable and low flow rates are usually a requirement for sufficient separation.
U.S. Pat. No. 3,095,371 describes a centrifuge having a gas vent. The gas vent valve is a complex design in which a cylindrical valve body is arranged to open and close a valve seat under the centrifugal pressure of the operating separator.
DE 610305 discloses a separator having an arrangement for venting gas. It utilizes a spring-loaded sphere which is balanced by the inlet pressure of the separator.
There is however a need in the art for improved and simplified methods of for draining off gas from a centrifugal separator.